2 Answers
2

If you read sort's documentation, you will find that it returns the sorted list, and the input list is modified by side effects. It does not say that the argument list will contain the sorted result -- It is just somehow modified by the sorting algorithm. Or, to put it shortly: sort is destructive.

Also, note that modifying literals destructively may have consequences you don't expect. (See for example: stackoverflow.com/questions/6865142/…, which is about CL but applies to Emacs-Lisp, too)
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danleiAug 28 '11 at 20:05